In a wafer fabrication facility, virtually all of the stages involved in producing a final product are performed on a semiconducting wafer in an evacuated or low pressure chamber. Typically, during and/or after at least some of the stages, the surface of the wafer is inspected. The inspections verify that the wafer is correctly aligned, that expected changes on the surface of the wafer have in fact occurred, and that no unexpected changes have also occurred. The inspections are advantageously performed while the wafer remains in its chamber, and typically so that the chamber remains in substantially the same evacuated or low pressure state used for implementing a stage prior to inspection.
Methods for inspecting semiconducting wafer surfaces under evacuated or low pressure conditions are known in the art. For example, Serenity Technologies Inc., of Beaverton, Ore., produce an OPTIVAC™ viewer that is stated to be an entire optical microscope, including a Charged Couple Device (CCD), inside an ultra high vacuum environment. However, the inclusion of electronic parts inside a vacuum chamber is problematic due to space issues and possible contamination of the interior clean vacuum environment.
Notwithstanding the above, an improvement to inspection methods is desirable.